Wash and dry all produce. Adjust oven rack to upper position and preheat to 450 degrees. Finely chop chives. Cut potatoes into 1-inch pieces. Place potatoes and garlic cloves in a medium pot. Add enough water to cover by 2 inches. Season with a few large pinches of salt. Bring to a boil.

Cook potatoes until easily pierced, about 15 minutes, then drain and return to empty pot. Add Gruyère, Parmesan, 1/2 cup milk (we sent more), 2 TBSP butter, and half the chives (we’ll use the rest later). Mash with a potato masher or fork until smooth. Season with salt and pepper. Set aside, covered, until meal is ready.

While potatoes cook, toss carrots on a baking sheet with a large drizzle of oil, salt, and pepper. Roast in oven until tender, about 15 minutes, tossing halfway through. Meanwhile, halve, peel, and thinly slice onion.

Heat a large drizzle of olive oil in a large pan over medium heat (use a nonstick pan if you have one). Add onion, dried cherries, and a pinch of salt. Cook, stirring occasionally, until onions are deeply browned, about 10 minutes. (TIP: Add a little water as needed to keep onions from burning.) Remove from pan and set aside. Pat steak dry with a paper towel. Season all over with salt and pepper.

Heat another drizzle of olive oil in same pan over medium-high heat. Add steak and cook to desired doneness, 4-6 minutes per side. Transfer to a cutting board to rest. Add 1/4 cup water, stock concentrate, vinegar, and cherry jam to pan and stir, scraping up any browned bits on bottom. Bring to a simmer, then stir in onion and cherries. Simmer until just thickened, about 1 minute.

Remove pan from heat and stir in 1 TBSP butter. Season with salt and pepper. Divide steak between plates. (TIP: Slice it first against the grain for easier eating.) Spoon cherry sauce over. Serve with potatoes and carrots on the side. Garnish with remaining chives.